Simultaneous and dynamic determination of longitudinal and transversal relaxation times of a nuclear spin system

Abstract

The invention relates to a magnetic resonance imaging method for simultaneous and dynamic determination of a longitudinal relaxation time T 1 and a transversal relaxation time T 2 of the nuclear spin system of an object, in the context of DCE or DSE MRI. In this respect, the invention makes use of a steady-state gradient echo pulse sequence comprising an EPI readout module.

The invention claimed is: 
     
       1. A magnetic resonance imaging method permitting simultaneous determination of a longitudinal relaxation behavior (R 1 ) and a transversal relaxation behavior (R 2 , R 2 *) of the nuclear spin system of an object, the method comprising:
 exciting the nuclear spin system of an object by applying a steady-state gradient-echo pulse sequence with a magnetic resonance imaging system, wherein said steady-state gradient-echo pulse sequence comprises:
 a series of RF excitation pulses that drive the nuclear spin magnetization up to a steady-state level, wherein each of said RF excitation pulses of the series, is followed by a multi gradient echo readout train, that generates multiple gradient echoes, 
 
 wherein the magnetic resonance imaging method further comprises:
 acquiring with said magnetic resonance imaging system MR signal data resulting from said applied gradient echoes in between the application of subsequent RF excitation pulses in the series of the steady-state gradient-echo pulse sequence; and 
 reconstructing, with a computer processor of said magnetic resonance imaging system, from said acquired MR signal data occurring at a first point in time, a first dynamic multi-gradient-echo data set, and a second dynamic multi-gradient echo data set occurring at a second point in time, 
 
 wherein with said computer processor of the magnetic resonance imaging system, the method further comprises:
 (a) determining from the reconstructed first dynamic multi-gradient-echo data set, baseline transversal relaxation behavior (R 2 , R 2 *) of the nuclear spin system and a baseline equilibrium magnetization of the nuclear spin system, 
 (b) determining from the reconstructed second dynamic multi-gradient-echo data set, an equilibrium magnetization of the nuclear spin system, 
 (c) determining further from the reconstructed second dynamic multi-gradient-echo data set, a dynamic transversal relaxation behavior (R 2 , R 2 *) of the nuclear spin system, 
 (d) determining, from the determined baseline equilibrium magnetization of the nuclear spin system of (a), and the determined equilibrium magnetization of the nuclear spin system of (a), a dynamic longitudinal relaxation behavior (R 1 ) of the spin system and 
 (e) providing the measurements of: 1) the baseline transversal relaxation behavior (R 2 , R 2 *) of the nuclear spin system; 2) the baseline equilibrium magnetization of the nuclear spin system; 3) the equilibrium magnetization of the nuclear spin system; 4) the dynamic transversal relaxation behavior (R 2 , R 2 *) of the nuclear spin system; and 5) the dynamic longitudinal relaxation behavior (R 1 ) of the spin system, to either a user, a display, or a memory, wherein the determination of the dynamic longitudinal relaxation behavior (R 1 ) and the dynamic transversal relaxation behavior (R 2 , R 2 *) of the nuclear spin system of an object are determined simultaneously in a concurrent measurement by said computer processor of the magnetic resonance imaging system. 
 
 
     
     
       2. The method of  claim 1 , wherein the determination of the dynamic longitudinal relaxation behavior (R 1 ) further comprises using the determined equilibrium magnetization of the nuclear spin system in order to relate the determined equilibrium magnetization of the nuclear spin system with respect to the determined baseline equilibrium magnetization of the nuclear spin system and determining therefrom the dynamic longitudinal relaxation behavior (R 1 ). 
     
     
       3. The method of  claim 1 , wherein the steady-state multi gradient-echo pulse sequence is a spoiled steady-state gradient-echo pulse sequence, with said sequence comprising:
 spoiler gradients before the applied series of RF excitation pulses, wherein the spoiler gradients are applied after each multi gradient echo readout train. 
 
     
     
       4. The method of  claim 1 , wherein the steady-state multi gradient-echo pulse sequence of  claim 1 , is a T 1  weighted fast field echo pulse sequence. 
     
     
       5. The method of  claim 1 , further comprising a pharmacokinetic modeling of the dynamic change of the dynamic transversal (R 2 , R 2 *) and/or longitudinal (R 1 ) relaxation behavior over the series of RF excitation pulses. 
     
     
       6. The method of  claim 5 , wherein the magnetic resonance imaging method comprises: either a dynamic contrast enhanced or a dynamic susceptibility enhanced MRI method. 
     
     
       7. The method of  claim 1 , further comprising
 determining with said computer processor of the magnetic resonance imaging system, a baseline longitudinal relaxation behavior (R 1 ) of the nuclear spin system describing the longitudinal relaxation behavior (R 1 ) of the spin system in the absence of the steady-state multi gradient-echo pulse sequence, 
 wherein the method further comprises
 determining with said computer processor of the magnetic resonance imaging system, from said baseline longitudinal relaxation behavior (R 1 ) the dynamic longitudinal relaxation behavior (R 1 ) which is then provided to either a user, a display, or a memory. 
 
 
     
     
       8. The method of  claim 1 , further comprising
 determining with said computer processor of the magnetic resonance imaging system, the flip angle of the applied series of RF excitation pulses, 
 wherein said flip angle is employed in the determination of the dynamic longitudinal relaxation behavior (R 1 ), by said computer processor of the magnetic resonance imaging system, which is then provided to either a user, a display, or a memory. 
 
     
     
       9. A non-transitory computer readable medium comprising instructions that when executed by a computer perform the magnetic resonance imaging method of  claim 1 . 
     
     
       10. A magnetic resonance imaging (MRI) apparatus permitting simultaneous determination of a longitudinal relaxation behavior (R 1 ) and a transversal relaxation behavior (R 2 , R 2 *) of the nuclear spin system of an object, wherein the apparatus comprises:
 a magnetic resonance imaging scanner configured for acquiring magnetic resonance image data, wherein the MRI apparatus further comprises 
 a controller configured for controlling an MRI scanner operation of:
 exciting the nuclear spin system of an object by applying a steady-state gradient-echo pulse sequence with the MRI scanner, wherein said steady-state gradient-echo pulse sequence comprises:
 a series of small flip angle RF excitation pulses that drive the nuclear spin magnetization upto a steady-state level, wherein each of said RF excitation pulses of the series, is followed by a multi gradient echo readout train, that generates multiple gradient echoes; 
 
 acquiring with said MRI scanner, MR signal data resulting from said applied gradient echoes in between the application of subsequent RF excitation pulses in the series of the steady-state gradient-echo pulse sequence; and 
 
 wherein the MRI scanner, apparatus further comprises:
 a data reconstruction system configured for: reconstructing from said acquired MR signal data occurring at a first point in time, a first dynamic multi-gradient-echo data set and a second dynamic multi-gradient echo data set occurring at a second point in time, 
 
 wherein with said computer processor of the MRI scanner performing the method steps of:
 (a) determining from the reconstructed first dynamic multi-gradient-echo data set, baseline transversal relaxation behavior (R 2 , R 2 *) of the nuclear spin system and a baseline equilibrium magnetization of the nuclear spin system, 
 (b) determining from the reconstructed second dynamic multi-gradient-echo data set, a dynamic transversal relaxation behavior (R 2 , or R 2 *) of the nuclear spin system, the spin system, 
 (c) determining further from the reconstructed second dynamic multi-gradient-echo data set, an equilibrium magnetization of the nuclear spin system, 
 (d) determining, from the determined baseline equilibrium magnetization of the nuclear spin system of (a), and the determined equilibrium magnetization of the nuclear spin system of (a), a dynamic longitudinal relaxation behavior (R 1 ) of the spin system and 
 (e) providing the measurements of: 1) the determined baseline transversal relaxation behavior (R 2 , R 2 *) of the nuclear spin system; 2) the determined baseline equilibrium magnetization of the nuclear spin system; 3) the determined dynamic transversal relaxation behavior (R 2 , R 2 *) of the nuclear spin system, 4) the determined equilibrium magnetization of the nuclear spin system; and 5) the determined dynamic longitudinal relaxation behavior (R 1 ) of the spin system, either to a user, a display, or a memory, wherein the determination of the dynamic longitudinal relaxation behavior (R 1 ) and the dynamic transversal relaxation behavior (R 2 , R 2 *) of the nuclear spin system of an object is determined simultaneously in a concurrent measurement by said computer processor of the MRI scanner.